Transport refrigeration system with co2 scrubber

ABSTRACT

A transport refrigeration system (TRS) for an enclosed space of a transport unit that includes a ventilation pathway to direct air to flow from the enclosed space. The TRS includes a refrigerant circuit with an evaporator configured to cool the air, and a CO2 scrubber. The CO2 scrubber includes a metal organic framework (MOF) configured to adsorb CO2 from the air in an adsorption mode and is regenerated with ambient air in a regeneration mode. A transport unit includes an enclosed space for storing produce, a ventilation pathway, and a TRS. A method of conditioning an enclosed space of a transport unit includes operating a TRS in a first mode that cools air from the enclosed space and adsorbs, with a MOF in a CO2 scrubber, CO2 from the air, and operating the TRS in a second mode that regenerates the MOF with ambient air.

FIELD

This disclosure relates generally to transport refrigeration systems.More specifically, this disclosure relates to CO₂ scrubbing transportrefrigeration systems.

BACKGROUND

Transport units are used to transport cargo across various distances.Transport units can include a transport refrigeration system tocondition the transport unit so that the cargo is kept at the desiredconditions during transport. Some transport units can be used totransport produce such as fruits and vegetables. The transportrefrigeration systems can be used to keep the air within the transportunit at desired temperature/range and/or CO₂ concentration/range to keepthe produce fresh during transport. In particular, marine transportrefrigeration systems used in marine transport units, which are used fortransporting cargo by boat (e.g., by water, sea), can be used to keepproduce more fresh during longer transport times.

BRIEF SUMMARY

In an embodiment, a transport refrigeration system (TRS) is for atransport unit that includes an enclosed space for storing produce and aventilation pathway. The TRS includes a refrigerant circuit and an CO₂scrubber. The ventilation pathway has an inlet and an outlet that areeach connected to the enclosed space of the transport unit. Air from theenclosed space is configured to enter the ventilation pathway throughthe inlet and be discharged from the ventilation pathway through theoutlet. The refrigerant circuit includes a compressor, a condenser, anexpander, and an evaporator that are fluidly connected. The evaporatoris disposed in the ventilation pathway and is configured to cool air asit flows through the ventilation pathway. The CO₂ scrubber contains ametal organic framework (MOF) configured to adsorb CO₂. The CO₂ scrubberis disposed in the ventilation pathway downstream of the evaporator. TheCO₂ scrubber has an adsorption mode and a regeneration mode. In theadsorption mode, the air cooled by the evaporator flows over the MOF andthe MOF adsorbs CO₂ from the air. In the regeneration mode, ambient airflows over the MOF and the adsorbed CO₂ in the MOF is desorbed into theambient air.

In an embodiment, the transport refrigeration system is configured todecrease a concentration of CO₂ in the enclosed space using the CO₂scrubber and without supplying ambient air into the enclosed space.

In an embodiment, the transport refrigeration system is configured toadjust a concentration of oxygen in the enclosed space by supplyingambient air into the enclosed space.

In an embodiment, the CO₂ scrubber is configured to maintain aconcentration of the CO₂ in the enclosed space within a predeterminedrange.

In an embodiment, the predetermined range is at or above 5% by volume ofthe CO₂ and at or less than 15% by volume of the CO₂.

In an embodiment, the predetermined range is based on a type of theproduce.

In an embodiment, the transport refrigeration system also includes aheater for heating the ambient air. In the regeneration mode, the heaterheats the ambient air prior to flowing over the MOF.

In an embodiment, the MOF has a maximum CO₂ saturation. The MOF isconfigured to desorb at least 90% of the maximum CO₂ saturation usingthe ambient air at a temperature at or below 70° C. degrees.

In an embodiment, the MOF has a CO₂ adsorption capacity of at least 25cm³ STP of CO₂/gram of MOF at a CO₂ concentration of 15 vol %.

In an embodiment, the CO₂ scrubber includes a MOF composition comprisingthe MOF and 1-10 wt % of binder.

In an embodiment, the binder is polyvinyl butyral.

In an embodiment, the MOF in the CO₂ scrubber is in a form of one ormore of pellets, a coating on a mesh, and a coating on a solid surface.

In an embodiment, the transport refrigeration system is a marinetransport refrigeration system and the transport unit is a marinetransport unit.

In an embodiment, a transport unit includes an enclosed space forstoring produce and a transport refrigeration system configured tocondition the enclosed space. The transport refrigeration systemincludes a ventilation pathway, a refrigerant circuit, and a CO₂scrubber. The ventilation pathway has an inlet and an outlet eachconnected to the enclosed space of the transport unit. The ventilationpathway is configured to direct air to flow from the enclosed space intothe ventilation pathway via the inlet and out of the ventilation pathwaythrough the outlet. The refrigerant circuit includes a compressor, acondenser, an expander, and an evaporator that are fluidly connected.The evaporator is disposed in the ventilation pathway and is configuredto cool the air flowing through the ventilation pathway. The CO₂scrubber is disposed in the ventilation pathway downstream of theevaporator. The CO₂ scrubber contains a metal organic framework (MOF)configured to adsorb CO₂. The CO₂ scrubber is configured to have anadsorption mode and a regeneration mode. The adsorption mode directs theair in the ventilation pathway to flow over the MOF which adsorbs CO₂from the air. The regeneration mode directs ambient air to flow over theMOF. The CO₂ adsorbed in the MOF is desorbed into the ambient air.

In an embodiment, the transport refrigeration system is configured todecrease a concentration of CO₂ in the enclosed space using the CO₂scrubber and without supplying ambient air into the enclosed space.

In an embodiment, the CO₂ scrubber is configured to maintain aconcentration of the CO₂ in the enclosed space within a predeterminedrange.

In an embodiment, the MOF has a maximum CO₂ saturation, and the MOF isconfigured to desorb at least 90% of the maximum CO₂ saturation usingthe ambient air at a temperature at or below 70° C. degrees.

In an embodiment, the MOF has a CO₂ adsorption capacity of at least 25cm³ STP of CO₂/gram at a CO₂ concentration of 15 vol %.

In an embodiment, a method is directed to conditioning an enclosed spaceof a transport unit. The enclosed space is for storing produce. Themethod includes operating a transport refrigeration system (TRS) in afirst mode and operating the TRS in a second mode. The TRS includes arefrigerant circuit and a CO₂ scrubber. The refrigerant circuit includesa compressor, a condenser, an expander, and an evaporator that arefluidly connected. The CO₂ scrubber includes a metal organic framework(MOF) configured to adsorb CO₂. Operating the TRS in the first modeincludes directing air from the enclosed space through a ventilationpathway, cooling the air flowing through the ventilation pathway withthe evaporator, and the MOF of the CO₂ scrubber absorbing the CO₂ fromthe air cooled by the evaporator. Operating the TRS in the second modeincludes directing ambient air through the CO₂ scrubber, andregenerating, with the ambient air, the MOF of the CO₂ scrubber. The CO₂adsorbed into the MOF in the first mode is released into the ambient airin the second mode.

In an embodiment, the operating in the first mode includes the CO₂scrubber operating in an adsorption mode, and the operating in thesecond mode includes the CO₂ scrubber operating in a regeneration mode.

In an embodiment, the operating of the TRS in the first mode does notadd ambient air into the enclosed space.

In an embodiment, the MOF has a CO₂ adsorption capacity of at least 25cm³ STP of CO₂/gram at a CO₂ concentration of 15 vol %.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of a refrigerant circuitof a marine transport refrigeration system.

FIG. 2 is a schematic diagram of an embodiment of a marine transportunit including a marine transport refrigeration system.

FIG. 3A is a schematic diagram of a CO₂ scrubber of the marine transportrefrigeration system in FIG. 2 operating in a first mode, according toan embodiment.

FIG. 3B is a schematic diagram of the CO₂ scrubber of the marinetransport refrigeration system in FIG. 2 operating in a second mode,according to an embodiment.

FIG. 4 is a block flow diagram of an embodiment of a method ofconditioning an enclosed space of a marine transport unit.

Like reference numbers represent like parts throughout.

DETAILED DESCRIPTION

A transport refrigeration system (TRS) can be used to condition (e.g.,cool, heat, remove CO₂ from, etc.) an enclosed space of the transportunit. In particular, the transport refrigeration system can be a marinetransport refrigeration system (MTRS) that conditions the enclosed spaceof a marine transport unit. The TRS can be configured to cool theenclosed space so that cargo contained within is at a desiredtemperature/range. In particular, the TRS can be configured to maintainthe CO₂ within the enclosed space at or within a specific range whentransporting produce such as fruits and vegetables. In some conventionalconfigurations air is added to the enclosed space to lower the CO₂concentration inside the enclosure to be within the desired range forthe produce being transported. However, this generally causes asignificant increase in the oxygen concentration within the containercausing the produce to have increased respiration. This increasedrespiration causing the produce to ripen more quickly, which isundesirable during transport.

Embodiments described herein are directed to transport refrigerationsystems, transport units including a transport refrigeration system, andmethods of conditioning an enclosed space of a transport unit that areable to conditioning the enclosed space, which includes cooling andmaintaining a desired CO₂ concentration, without significantlyincreasing the oxygen concentration (e.g., without adding oxygen). Forexample, the transport refrigeration systems and the methods ofconditioning are capable of removing CO₂ from the enclosed space tomaintain the desired CO₂ concentration without adding/suppling ambientair into the enclosed space. In some embodiments, the transportrefrigeration unit is a marine transport refrigeration system (MTRS)that conditions the enclosed space of a marine transport unit.

FIG. 1 is a schematic diagram of a refrigeration circuit 5 of a marinetransport refrigeration system 1, according to an embodiment. Therefrigeration circuit 5 includes a compressor 10, a condenser 20, anexpansion device 30, and an evaporator 40. In an embodiment, therefrigeration circuit 5 can be modified to include additionalcomponents. For example, the refrigeration circuit 5 in an embodimentcan include an economizer heat exchanger, one or more flow controldevices, a receiver tank, a dryer, a suction-liquid heat exchanger, orthe like.

The components of the refrigeration circuit 5 are fluidly connected. Themarine transport refrigeration system 1 can be configured as a coolingsystem that can be operated in a cooling mode, and/or marine transportrefrigeration system can be configured to operate as a heat pump systemthat can run in a cooling mode and a heating mode.

The refrigeration circuit 5 applies known principles of gas compressionand heat transfer. The heat transfer circuit can be configured to heator cool a process fluid (e.g., water, air, or the like). In anembodiment, the refrigeration circuit 5 may represent a chiller thatcools a process fluid such as water or the like. In an embodiment, therefrigeration circuit 5 may represent an air conditioner and/or a heatpump that cools and/or heats a process fluid such as air, water, or thelike.

During the operation of the refrigeration circuit 5, a working fluid(e.g., refrigerant, refrigerant mixture, or the like) flows into thecompressor 10 from the evaporator 40 in a gaseous state at a relativelylower pressure. The compressor 10 compresses the gas into a highpressure state, which also heats the gas. After being compressed, therelatively higher pressure and higher temperature gas flows from thecompressor 10 to the condenser 20. In addition to the working fluidflowing through the condenser 20, a first process fluid PF₁ (e.g.,ambient air, external water, or the like) also separately flows throughthe condenser 20. The first process fluid absorbs heat from the workingfluid as the first process fluid PF₁ flows through the condenser 20,which cools the working fluid as it flows through the condenser. Theworking fluid condenses to liquid and then flows into the expansiondevice 30.

The expansion device 30 allows the working fluid to expand, whichconverts the working fluid to a mixed vapor and liquid state. An“expansion device” as described herein may also be referred to as anexpander. In an embodiment, the expander may be an expansion valve,expansion plate, expansion vessel, orifice, or the like, or other suchtypes of expansion mechanisms. It should be appreciated that theexpander may be any type of expander used in the field for expanding aworking fluid to cause the working fluid to decrease in temperature. Therelatively lower temperature, vapor/liquid working fluid then flows intothe evaporator 40. A second process fluid PF₂ (e.g., air, water, or thelike) also flows through the evaporator 40. The working fluid absorbsheat from the second process fluid PF₂ as it flows through theevaporator 40, which cools the second process fluid PF₂ as it flowsthrough the evaporator 40. As the working fluid absorbs heat, theworking fluid evaporates to vapor. The working fluid then returns to thecompressor 10 from the evaporator 40. The above-described processcontinues while the refrigerant circuit 5 is operated, for example, in acooling mode.

The marine transport refrigeration system 1 can also include acontroller 90. In an embodiment, the controller 90 may be the controllerof the marine transport refrigeration system 1. In an embodiment, thecontroller 90 may be the controller of the refrigerant circuit 5. Forexample, the controller 90 may be the controller of the compressor 10.Dotted lines are provided in the Figures to indicate fluid flows throughthe heat exchangers (e.g., condenser 20, evaporator 40), and should beunderstood as not specifying a specific path of flow through each heatexchanger. Dashed dotted lines are provided in the Figures to illustrateelectronic communications between different features. For example, adashed dotted line extends from a controller 90 to the compressor 10 asthe controller 90 is able to control and operate the compressor 10(e.g., control a speed of the compressor). For example, a dashed-dottedline extends from the controller 90 to the expansion valve 30 as thecontroller 90 controls the heater 30. In an embodiment, the controller90 includes memory (not shown) for storing information and a processor(not shown). The controller 90 in FIG. 1 and described below isdescribed/shown as a single component. However, it should be appreciatedthat a “controller” as shown in the Figures and described herein mayinclude multiple discrete or interconnected components that include amemory (not shown) and a processor (not shown) in an embodiment.

FIG. 2 illustrates a schematic view of a marine transport unit 100,according to an embodiment. The marine transport unit 100 includes atransport container 102 with an enclosed space 104 for storing cargo106. The cargo 106 is produce, such as fruits and vegetables, whichgenerate and exhaust CO₂ into the enclosed space 104 over time throughaerobic respiration. Over time, this respiration increases the CO₂concentration in the air within the enclosed space 104. The marinetransport unit 100 also includes a ventilation pathway 110 for directingair to and from the enclosed space 104. For example, air from theenclosed space 104 is cycled through the ventilation pathway 110. Thisair flowing from the enclosed space 104 into the ventilation pathway 110may also be referred to as indoor air.

The marine transport unit 100 includes a marine transport refrigerationsystem 120 configured to condition the enclosed space 104. Theventilation pathway 110 has an inlet 112 and an outlet 114 that are eachconnected to the enclosed space 104. The air from within the enclosedspace 104 is suctioned into the inlet 112, flows through the ventilationpathway 110, and is discharged from the outlet 114 back into theenclosed space 104. For example, the marine transport unit 100 mayinclude one or more fans 126 that direct air to flow through theventilation pathway 110 and out through the outlet 114 into the enclosedspace 104. The marine transport refrigeration system 120 conditions theair as it travels through the ventilation pathway 110, which thenconditions the enclosed space when the conditioned air is dischargedback into the enclosed space 104.

The marine transport refrigeration system 120 includes a refrigerationcircuit 122 and a CO₂ scrubber 140. In an embodiment, the refrigerationcircuit 122 in FIG. 2 may be the refrigeration circuit 5 in FIG. 1 . Therefrigeration circuit 122 includes an evaporator 124. The evaporator 124and the CO2 scrubber 140 are disposed in the ventilation pathway 110. Asshown in FIG. 2 , The air in the ventilation pathway 110 passes throughthe evaporator and through the CO₂ scrubber 140 as it flows through theventilation pathway 110. As shown in FIG. 2 , the air flows through theevaporator 124 and then through the CO₂ scrubber 140 as the air flowsthrough the ventilation pathway 110 from the inlet 112 to the outlet114.

The evaporator 124 and the CO₂ scrubber 140 condition the air as itpasses through the ventilation pathway 110. The evaporator 124 cools theair passing through the ventilation pathway 110 (e.g., the air is cooledby the refrigerant in the evaporator 124 as the air and the refrigeranteach flow through the evaporator 124 without mixing).

The CO₂ scrubber 140 is configured to remove CO₂ from the air as itpasses through the ventilation pathway 110. The CO2 scrubber 140includes a metal organic framework (“MOF”) 142 (shown in FIGS. 3A and3B). The CO2 scrubber 140 is configured to have an adsorption mode and aregeneration mode. FIG. 2 shows the CO₂ scrubber 140 operating in anadsorption mode. In the adsorption mode, the CO₂ scrubber 140 directsthe air over the MOF 142 and the MOF 142 adsorbs CO₂ from the air. Inthe regeneration mode, the CO2 scrubber 140 directs ambient air from theambient environment 170 (e.g., from outside the transport container 102)over the MOF and the adsorbed CO₂ in the MOF 142 desorbs into theambient air. The ambient air containing the desorbed CO₂ is thendischarged back into the ambient environment 170. The operation of theCO₂ scrubber 140 is discussed in more detail below.

The MTRS 120 is configured to be able to condition the enclosed space104 without adding ambient air. In particular, the MTRS 120 isconfigured to cool the enclosed space 104 and regulate the CO₂concentration C₁ of the enclosed space 104 without adding ambient air.The MTRS 120 is configured to condition the enclosed space 104 so thatCO₂ concentration C₁ of the enclosed space 104 stays within apredetermined range. In an embodiment, the predetermined range for theCO₂ concentration is 5-15 vol %. In an embodiment, the predeterminedrange for the CO₂ concentration is 5-10 vol %. In an embodiment, thepredetermined range for the CO₂ concentration may be predetermined rangethat is based on the type of produce 106 being transported. In anembodiment, the controller 190 may be configured to determine the typeof produce 106 being transported (e.g., through user input,identification on the produce, or the like), and then use apredetermined range that corresponds to the type of produce 106 beingtransported.

Produce 106 produces CO₂ over time through respiration (e.g., aerobicrespiration). An increase in the concentration of oxygen within thecontainer can cause the produce to have increased respiration, whichresults in producing greater amounts of CO₂. For example, at a CO₂concentration of 10% by volume: a marine transport container of mangoscan produce about 200 liters/hour of CO₂, a marine transport containerof okra can produce about 425 liters/hour of CO₂, and a marine transportcontainer of garlic can produce about 80 liters/hour of CO₂. The MTRS120 is configured to remove CO₂ using the MOF 142 such that the CO₂concentration C₁ of the enclosed space 104 stays within a predeterminedrange. For example, the MTRS 120 may be configured to remove CO₂ at orabout the same rate at which the produce generates CO₂. The rate ismeasured over an extended period of time (e.g., at least 6 hours, atleast 12 hours, at least 1 day, etc.).

The MOF 142 is configured to be able to effectively reduce the CO₂ inthe cooled air discharged from the evaporator 124. In an embodiment, theCO₂ scrubber 140 has a maximum CO₂ adsorption rate that is equal to orgreater than the CO₂ production rate of any potential produce 106 to betransported in the marine transport unit 100.

In an embodiment, the marine transport refrigeration system 120 mayinclude a by-pass 160 configured to allow for a portion of the cooledair discharged from the evaporator 124 to by-pass the MOF 142. Forexample, the by-pass 160 may be an actuatable vent or the like. Theby-pass 160 can be used to decrease the amount of cooled air thatinteracts with the MOF 142. For example, the by-pass 160 may be adjusted(e.g., opened more, closed more, etc.) to adjust the amount of CO₂adsorbed from the cooled air by the CO₂ scrubber 140. The by-pass 160may be adjusted to control the CO₂ concentration C₂ of the conditionedair discharged into the enclosed space 104. For example, the controller190 may be configured to adjust the by-pass 160 based on the CO₂concentration C₁ within of the enclosed space 104 (e.g., such that theconditioning results in the CO₂ concentration C₁ being within thedesired amount/range). The by-pass 160 in FIG. 2 is shown as be externalto the CO₂ scrubber 140. However, it should be appreciated that theby-pass 160 in an embodiment may be provided within the CO₂ scrubber140. For example, the by-pass 160 within the CO₂ scrubber 140 may be aflow path that does not flow over or contact the MOF 142.

In an embodiment, the CO₂ scrubber 140 may be configured to beinterchangeable based on the type of produce 106 being transported. Forexample, a plurality of CO₂ scrubbers may be configured for eachrespectively used in the MTRS 120. Each of the CO₂ scrubbers in theplurality has a configuration for adsorbing the amount of CO₂ for arespective produce or for a range of produces. For example, a first CO₂scrubber is configured to adsorb CO₂ for transporting garlic as theproduce 106 in the transport unit 100 (e.g., configured to adsorb at orabout the rate at which a load of garlic produces CO₂, configured toabsorb at or about 80 liters/hour of CO₂), a second CO₂ scrubber isconfigured to adsorb CO₂ for transporting a load of mangos (e.g.,configured to adsorb at or about the rate at which a load of mangosproduces CO₂, configured to absorb at or about 200 liters/hour of CO₂),and a third CO₂ scrubber is configured to adsorb CO₂ for transporting aload of okra (e.g., configured to adsorb at or about the rate at which aload of okra produces CO₂, configured to absorb at or about 425liters/hour of CO₂). For example, each of the CO₂ scrubbers in pluralityof CO₂ scrubbers can have an amount of the MOF that results in the CO₂scrubber adsorbing CO₂ at or about the rate of its corresponding type ofproduce. In an embodiment, a method of conditioning the enclosed space104 may include determining the type of produce 106 to be transported inthe enclosed space 104, and installing the CO₂ scrubber 104 from aplurality of CO₂ scrubbers that corresponds to the type of produce 106being transported.

As shown in FIG. 2 , the MTRS 100 includes a controller 190. In anembodiment, the controller 190 may be the controller 90 of the MTRS 100.In an embodiment, the controller 190 may be a controller of therefrigerant circuit 122. The controller 190 can be configured to controlthe operation of the MTRS 100. The controller 190 can be configured tocontrol the MTRS 100 so that the enclosed space 104 is at the desiredconditions as described herein (e.g., desired CO₂ concentration/range,desired temperature). For example, the controller 190 may control theoperation of the refrigeration circuit 122 (e.g., control amount ofcooling provided by the evaporator 124), the operation of the CO₂scrubber 140 (e.g., amount of CO₂ removal provided by the CO₂ scrubber140), and the operation of the fan 126 (e.g., fan speed). The controller190 may use sensors (e.g., CO₂ concentration sensor 192A, temperaturesensor 192B, CO₂ concentration sensor 192C, temperature sensor 192D,oxygen sensor 192E, and the like) to detect for conditions of theenclosed space and/or operating conditions of the MTRS 100. For example,the controller 190 may use a CO₂ concentration sensor 192A to detect theCO₂ concentration C₁ of the air in the enclosed space 104, a temperaturesensor 192B to detect the temperature T₁ of the air in the enclosedspace 104, a CO₂ concentration sensor 192C to detect the CO₂concentration C₂ of the conditioned air being discharged into theenclosed space 104, a temperature sensor 192D to detect the temperatureT₂ of the conditioned air being discharged into the enclosed space 104,and/or an oxygen concentration sensor 192E to detect the oxygenconcentration C₃ of the air in the enclosed space 104. The controller190 can control and adjust the operation MTRS 100 based on the detectedthe conditions such that the enclosed space 104 is conditioned to be thedesired conditions as described herein.

FIGS. 3A and 3B is a schematic view of an embodiment of the CO₂ scrubber140 in FIG. 2 . FIG. 3A illustrates the CO2 scrubber in a first mode.FIG. 3B illustrates the CO2 scrubber 140 in a second mode. For example,the first mode is an adsorption mode and the second mode is aregeneration mode. In the illustrated embodiment, the CO2 scrubber 140includes the MOF 142, an indoor air inlet 144, an indoor air outlet 146,an ambient air inlet 148, and an ambient air outlet 150.

As shown in FIG. 3A, the CO₂ scrubber 140 in the first mode isconfigured to have the indoor air inlet 144 open, the indoor air outlet146 open, the ambient air inlet 148 closed, and the ambient air outlet150 closed. In the first mode, ambient air from the ambient environment170 does not flow into and/or through the CO₂ scrubber 140. In the firstmode, the CO₂ scrubber is configured to adsorb/remove CO₂ from thecooled air F_(CA) discharged from the evaporator 124 (shown in FIG. 2 ).The CO₂ scrubber 140 receives the cooled air F_(CA) via the indoor airinlet 144. The CO₂ scrubber 140 directs the air to flow over the MOF142. The MOF 142 adsorbing CO₂ from the air as the air flows over theMOF 142. The cooled, CO₂ scrubbed air F_(D) is then discharged from CO₂scrubber 140 through the indoor air outlet 146. As discussed above, thecooled, CO₂ scrubbed air then flows from the CO₂ scrubber 140 and isdischarged from the outlet 114 of the ventilation pathway 110 into theenclosed space 104.

When the MOF 142 is at a maximum CO₂ adsorption threshold, the CO₂scrubber 140 is configured to switch to the second mode (e.g.,illustrated in FIG. 3B) to regenerate the MOF 142. The maximum CO₂adsorption threshold is a predetermined saturation level. The maximumCO₂ adsorption threshold may be at or near the full saturation of theMOF 142 (e.g., at or near the CO₂ adsorption capacity of the MOF 142).In an embodiment, the maximum CO₂ adsorption threshold can be at orabove 90% of the CO₂ adsorption capacity of the MOF 142. In anembodiment, the maximum CO₂ adsorption threshold can be at or above 95%of the CO₂ adsorption capacity of the MOF 142.

As shown in FIG. 3B, the CO₂ scrubber 140 in the second mode isconfigured to direct ambient air F_(AI) from the ambient environment 170to pass over the MOF 142. The CO₂ scrubber 140 in the second mode isconfigured to have the indoor air inlet 144 closed, the indoor airoutlet 146 closed, the ambient air inlet 148 open, and the ambient airoutlet 150 open. Ambient air F_(AI) flows into the CO2 scrubber 140through the ambient air inlet 148, passes over the MOF 142, and thendischarged through the ambient air outlet 150. The ambient air F_(AI)has a lower content of CO₂ (e.g., at or about 0.03 vol % of CO₂), suchthat the adsorbed CO₂ in the MOF 142 desorbs into the ambient air as itpasses over the MOF 142. The ambient air containing the desorbed CO₂F_(AO) is then discharged from the CO₂ scrubber 140 through the ambientair outlet 150. For example, the mixture F_(AO) of ambient and desorbedCO₂ is discharged back into the ambient environment 170. The CO₂scrubber 140 is configured to remain in the second mode until the MOF142 reaches a minimum CO₂ adsorption threshold. For example, the minimumCO₂ adsorption threshold may be a predetermined threshold. In anembodiment, the minimum CO₂ adsorption threshold can be at or below 10%of the CO₂ adsorption capacity of the MOF 142. In an embodiment, theminimum CO₂ adsorption threshold can be at or below 5% of the CO₂adsorption capacity of the MOF 142.

In an embodiment, the marine transport refrigeration system 120 mayinclude a heater 152 configured to heat the ambient air F_(AI) used bythe CO₂ scrubber 140 in the second mode. In an embodiment, the heater152 may be an electric heater, a combustion heater, a heat exchanger, orthe like. In one embodiment, the heater 152 may be a heat exchangerconfigured to heat the ambient air F_(AI) using heat from therefrigerant circuit 122 (shown in FIG. 2 ). For example, the heater 152may be a heat exchanger in the refrigerant circuit 122 disposeddownstream of the compressor and upstream of the expander (e.g.,downstream of the compressor 10 and upstream of the expansion device 30in the refrigerant circuit 5 in FIG. 1 ), in which the flowingrelatively hotter, compressed refrigerant heats the flowing ambient airF_(AI) within the heat exchanger without physically mixing. The heater152 is configured to heat the ambient air F_(AI) before flowing over theMOF 142. In an embodiment, the heater 152 is configured to heat theambient air F_(AI) to a temperature at or above 45°. In an embodiment,the heater 152 is configured to heat the ambient air F_(AI) to atemperature of 50-70° C. The heated ambient air then flows over the MOF142. The heating by the heater 152 can increase the desorption rate ofthe CO₂ from the MOF 142 into the ambient air F_(AI) . In an embodiment,the MOF 142 can be fully regenerated (e.g., at least 95% of the adsorbedCO₂ desorbed, at least 98% of the adsorbed CO₂ desorbed) in less than 25minutes using the heated ambient air.

The air (e.g., cooled air in the first mode, ambient air in the secondmode) contacts the MOF 142 as it flows over the MOF 142. Air may flowover the MOF 142 by passing along an outer surface of the MOF 142 and/orby flowing through the MOF 142. For example, air may flow through theMOF 142 by flowing through a substrate on which the MOF 142 is disposed,by flowing through a MOF composition containing the MOF 142 (e.g., a MOFcomposition including MOF and a binder), or the like.

The CO₂ scrubber 140 is configured to adsorb CO₂ without adding ambientair to the enclosed space 104. Thus, CO₂ scrubber 140 can remove CO₂without significantly increasing the concentration of oxygen C₃ in theenclosed space 104. For example, the CO₂ scrubber 140 is configured tonot mix the ambient air and the indoor air (e.g., cooled air from theevaporator) during operation. The MTRS 120 is configured to decrease theCO₂ concentration C₁ within the enclosed space 104 (i.e., using the CO₂scrubber) without adding ambient air from the ambient environment 170 tothe enclosed space 104.

The MTRS 120 can also be configured to condition the enclosed space 104so that oxygen concentration C₃ of the enclosed space 104 is at or abovea predetermined minimum. In an embodiment, the predetermined minimum forthe oxygen concentration may be a predetermined minimum that is based onthe type of produce 106 being transported. In an embodiment, thecontroller 190 may be configured to determine the type of produce 106being transported (e.g., through user input, identification on theproduce, or the like), and then use a predetermined minimum thatcorresponds to the type of produce 106 being transported. In anembodiment, the predetermined minimum may at or about 1 vol % of oxygenfor the air in the enclosed space 104. In an embodiment, thepredetermined minimum may be at or about 2 vol % of oxygen for the airin the enclosed space 104. In an embodiment, the predetermined minimummay be at or about 10 vol % of oxygen for the air in the enclosed space104. In an embodiment, the MTRS 120 can also be configured to maintainthe oxygen vol % of oxygen for the air in the enclosed space 104 below apredetermined maximum concentration (e.g., at or below atmospheric, ator below 21 vol % of oxygen).

In an embodiment, the MTRS 120 is configured to supply ambient air intothe enclosed space 104 to adjust the oxygen concentration C₃ of the airwithin the enclosed space 104 (e.g., to increase the oxygenconcentration C₃ of the air within the enclosed space 104). Supplyingambient air into the enclosed space 104 can increase the oxygenconcentration C₃ of the air within the enclosed space 104. The MTRS 120supplies ambient air into the enclosed space based on the oxygenconcentration of the air within the enclosed space. to The MTRS 120 mayinclude an ambient air inlet 116 for supplying the ambient air into theenclosed space 104. For example, the ambient air inlet 116 can be anactuatable vent or the like that can be actuated between open andclosed. The MTRS 120 can operate the ambient air inlet 116 (i.e., openand close the ambient air inlet 116, turn on/off a fan in the ambientair inlet (not shown), or the like). When open, ambient air from theambient environment 170 flows through the ambient air inlet 116 into thetransport container 102. When closed, ambient air is blocked and doesnot flow through the ambient air inlet 116 into the transport container102. As shown in FIG. 2 , the ambient air inlet 116 is connected to theventilation pathway 110 to allow for cooling of the air by theevaporator 124. In an embodiment, the ambient air inlet 116 may beconfigured to discharge directly into the enclosed space 104.

In FIGS. 3A and 3B, the CO₂ scrubber 140 is shown as only have a singlecompartment/cartridge of the MOF 142. However, in an embodiment, the CO₂scrubber 140 may include multiple cartridges of the MOF 142. In such anembodiment, the CO₂ scrubber may be configured to operate the cartridgesin different modes during operation. For example, the CO₂ scrubberoperates a first cartridge of the MOF 142 in the first mode (e.g., theMOF 142 in the first cartridge contacting and adsorbing CO₂ from thecooled air F_(CA)) while operating a second cartridge of the MOF 142 inthe second mode (e.g., the MOF 142 in the second cartridge contactingthe ambient air F_(AI) and desorbing the adsorbed CO₂ into the ambientair F_(AI)). The CO₂ scrubber may then operate the second cartridge ofthe MOF 142 in the first mode while operating the first cartridge of theMOF 142 in the second mode. In such an embodiment, it should beappreciated that the CO₂ scrubber 140 can includevalve(s)/duct(s)/blower(s) to direct the ambient air and cooled air topass through their respective cartridge(s) without being mixed. Thisconfiguration can allow the CO₂ scrubber to continuously operate as atleast one of the cartridges of MOF 142 is available to scrub the air.

The CO2 scrubber 140 includes the MOF 142. The MOF 142 includes metalions, and/or clusters of metal ions, bound together with an organiclinker (e.g., organic ligand, or the like). In an embodiment, the MOF142 is a hydrophobic MOF. The MOF is configured to adsorb while havinglimited absorption other components from the air. For example, the MOF142 is configured to adsorb less than 5 vol % of non-CO₂ components whenat or about full CO₂ saturation. In an embodiment, the metal ions in theMOF 142 include potassium and cobalt and the organic linker is citratelinker. For example, the MOF 142 can be K₂Co₃(cit)₂, cit=C₆H₄O₇.

In an embodiment, the MOF 142 has a CO₂ adsorption capacity of at least25 cm³ STP/g (i.e., adsorbs 25 cm³ of CO₂ at the standard pressure andtemperature (STP) of 0° C. and 1 atm per gram of MOF), when adsorbingCO₂ from air containing 15 vol % of CO₂. In an embodiment, the MOF 142has a CO₂ adsorption capacity of at least 30 cm³ STP/g (i.e., adsorbs 30cm³ of CO₂ at the standard pressure and temperature (STP) of 0° C. and 1atm per gram of MOF), when adsorbing CO₂ from air containing 15 vol % ofCO₂. In an embodiment, the MOF 142 has a CO₂ adsorption capacity atleast 35 cm³ STP/g, when adsorbing CO₂ from air containing 15 vol % ofCO₂. In an embodiment, the MOF 142 has a CO₂ adsorption capacity atleast 40 cm³ STP/g, when adsorbing CO₂ from air containing 15 vol % ofCO₂.

The MOF 142 may be used in a variety of different forms. The MOF 142 canbe applied as a MOF composition that includes the MOF and a binder. TheMOF composition may be in the form of a coating, a pellet, or the like.In an embodiment, MOF composition is in the form of a coating applied toone or more solid and/or mesh surfaces (e.g., metal surfaces, plasticsurfaces, mesh surfaces, etc.). For example, the coating may be appliedto a structure having high surface area (e.g., a hollow honeycombstructure, a fluted structure, or the like) to have a maximum/largesurface for adsorption. In an embodiment, the MOF composition in theform of pellets. In an embodiment, the pellets are formed to have asubstantially spherical shape (e.g., having at least one of a sphericalshape and a semi-spherical shape). In an embodiment, the pellets had anaverage width (e.g., average diameter) of 3-6 mm. 1 mm to 5 mm

The pellets are made of a MOF composition that includes the MOF and abinder. The binder adheres the MOF to itself and into the pellet shape.The binder is configured to adhere the MOF while having a limited impacton the CO₂ adsorption capacity of the MOF. In an embodiment, the binderis configured to decrease the CO₂ adsorption capacity of the MOF by lessthan 15% (e.g., CO₂ adsorption capacity of the MOF composition ≥85% ofCO₂ adsorption capacity of pure MOF). Adsorption capacity refers to themaximum amount of CO₂ (e.g., cm³/g) that a material is capable ofadsorbing.

In an embodiment, the binder in the MOF composition is polyvinyl butyral(PVB). For example, PVB has been found to have provide goodadhesion/cohesion for the MOF while having a limited impact on itsadsorption capacity. In an embodiment, the MOF composition contains 1-10wt % of the binder. In an embodiment, the MOF composition contains 2-8wt % of the binder. In an embodiment, the MOF composition contains 2-6wt % of the binder. In an embodiment, the MOF composition contains 3-5wt % of the binder. For example, in one embodiment, an MOF compositioncontaining 4.1 wt % of PVB as the binder was found to provide highadhesion while only decreasing the CO₂ adsorption capacity of the MOF byabout 11.6%. For example, in another embodiment, an MOF compositioncontaining 2.0 wt % of PVB as binder provided adequate adhesion whileonly decreasing the CO₂ adsorption capacity of the MOF by about 1.5%.

FIG. 4 is a block flow diagram of a method 1000 of conditioning anenclosed space of a marine transport unit. In an embodiment, the method1000 may be applied using the marine transport refrigeration system(MTRS) 120 of the marine transport unit 100 in FIG. 2 . In anembodiment, the method 1000 may be employed using the MTRS 1 in FIG. 1 .For example, the marine transport unit can include a marine transportrefrigeration system (MTRS) (e.g., MTRS 120) that includes an evaporator(e.g., evaporator 40, evaporator 124) and a CO₂ scrubber (e.g., CO2scrubber 140). the method 1000 may be carried out by a controller (e.g.,controller 190) of the marine transport unit 100 to condition theenclosed space 104 the marine transport unit 100. The method 1000 beginsat 1010.

At 1010, the MTRS is operated in a first mode. For example, the firstmode is a cooling and CO₂ adsorption mode (e.g., as shown in FIGS. 2 and3A) that is configured to cool and remove CO₂ from the air of theenclosed space (e.g., enclosed space 104). The MTRS in the first modecan be configured to discharged the conditioned air back into theenclosed at a temperature (e.g., temperature T₂) and a CO₂ concentration(e.g., CO₂ concentration C₂ of the air) such that the enclosed space isat a desired temperature point/range and a desired CO₂ concentration asdiscussed above. As shown in FIG. 4 , operating the MTRS in the firstmode includes 1012, 1014, and 1016.

At 1012, air from the enclosed space is directed through a ventilationpathway (e.g., ventilation pathway (e.g., ventilation pathway 110). Theventilation pathway including an inlet (e.g., inlet 112) and an outlet(e.g., outlet 114) connected to the enclosed space. Directing air fromthe enclosed space through a ventilation pathway at 1012 can includeoperating one or more fans (e.g., fan 126) to blow the air through theventilation pathway. For example, operating the fan(s) can includeoperating each of the fan(s) at a speed based on the desiredconditioning for the enclosed space.

At 1014, evaporator cools the air flowing through the ventilationpathway. Cooling that air at 1014 can include detecting a temperature ofthe enclosed space (e.g., temperature T₁) and operating the evaporatorto provide an amount of cooling to the air based on the detectedtemperature of the enclosed space (e.g., so that the enclosed space isconditioned to a desired temperature/range). For example, this caninclude operating a refrigerant circuit of the evaporator (e.g.,refrigerant circuit 5, refrigerant circuit 122) so that the refrigerantflowing through the evaporator provides said amount of cooling to theair.

At 1016, the CO₂ scrubber adsorbs CO₂ from the air cooled by theevaporator. This can be referred to as operating the CO₂ scrubber in anadsorption mode. The CO₂ scrubber adsorbing CO₂ from the air cooled bythe evaporator includes directing the cooled air discharged from theevaporator across a MOF (e.g., MOF 142) within the CO₂ scrubber and theMOF adsorbs the CO₂ from the air. In an embodiment, adsorbing CO₂ fromthe air with the CO₂ scrubber at 1016 can include adsorbing an amount ofCO₂ from the air based on the concentration of CO₂ in the air theenclosed space 1017A (e.g., CO₂ concentration C₁) and a predeterminedCO₂ concentration range for the air in the enclosed space 1017B (e.g., apredetermined desired CO₂ concentration range for the produce 106). Inan embodiment, the CO₂ scrubber may be configured to adjust the amountof CO₂ adsorbed by MOF by exposing less of the MOF to the cooled air(e.g., less exposure to decreases the amount of amount of CO₂ adsorbed).For example, this may include by passing a portion of the cooled airaround the MOF 142 (e.g., through by-pass 160). For example, this mayinclude increasing a flow rate of the air through the scrubber (e.g.,increasing speed of fan 126) such that the degree of contact between thecooled air and the MOF is decreased. In the first mode, the cooled andCO2 scrubbed air can then be discharged back into the enclosed space104. The method 1000 then proceeds from 1010 to 1020.

At 1020, the MTRS is operated in a second mode. For example, the secondmode is a regeneration mode for the MOF in the CO₂ scrubber. In anembodiment, the MTRS is configured to change from the first mode to thesecond mode when the MOF in the CO₂ scrubber is at a maximum CO₂adsorption threshold (e.g., a predetermine saturation level, apredetermined saturation at or near maximum saturation). Operating theMTRS in the second mode 1020 includes 1022 and 1024.

At 1022, ambient air (e.g., ambient air FAT) is directed through the CO₂scrubber. The ambient air is directed at 1022 to flow over the MOF usedto adsorb CO₂ at 1016. The ambient air is directed through the CO₂scrubber at 1022 without mixing with air flowing to and/or from theenclosed space (e.g., cooled air discharged from the evaporator). In anembodiment, directing the ambient air through the CO₂ scrubber at 1022includes directing the ambient air from the ambient environment (e.g.,ambient environment 170) to the CO₂ scrubber, directing the ambient airto flow over the MOF, and discharging the air after flowing over the MOFback into the ambient environment (e.g., ambient environment 170).

In an embodiment, directing the ambient air through the CO₂ scrubber at1022 may include heating the ambient air with a heater (e.g., heater152). The ambient air is heated before flowing over the MOF and theheated ambient air flows over the MOF. For example, ambient air isdirected from the ambient environment through the heater, and then theheated ambient air is directed from the heater 152 to and over the MOF.

At 1024, the ambient air regenerates the MOF. The ambient airregenerates the MOF at 1024 by the adsorbed CO₂ in the MOF desorbinginto the ambient air as it flows over the MOF. This can be referred tooperating the CO₂ scrubber in regeneration mode. In an embodiment,heated ambient air flows over the MOF. The temperature increase of theambient air can increase the rate at which the CO₂ in the MOF desorbsinto the ambient air (e.g., increases the CO₂ desorption rate from theMOF).

In an embodiment, operating in the second mode 1020 may also optionallyinclude 1026. At 1026, air from the enclosed space is directed throughthe ventilation pathway and the air is conditioned as it flows throughthe ventilation pathway. The air is directed through the ventilationpathway at 1026 without mixing with the ambient air being directedthrough the CO₂ scrubber at 1022. For example, in an embodiment, the airis directed through the ventilation pathway at 1026 by being by-passedaround the CO₂ scrubber (e.g., through by-pass 160).

In an embodiment, the CO₂ scrubber may include multiplecompartments/cartridges of the MOF as discussed above. For example, theambient air is directed through a first cartridge of the MOF at 1022 andthe air flowing through the ventilation pathway at 1026 may be directedthrough a second cartridge of the MOF such that the ambient air and theair from the enclosed space do not mix. In such an embodiment, operatingin the first mode at 1010 may include directing ambient air through thesecond cartridge of the MOF to regenerate the MOF in the secondcartridge similar to 1022 and 1024, except for a regenerating the secondcartridge of the MOF.

In an embodiment, operating in the second mode 1020 may also optionallyinclude 1028. At 1028, ambient air is supplied from the ambientenvironment into the enclosed space (e.g., ambient air through theambient air inlet 116). The ambient air is supplied to the enclosedspace at 1028 to decrease the concentration of oxygen (e.g., oxygenconcentration C₃) within the enclosed space. The ambient air is not theambient air directed and used to regenerate the MOF at 1022 and 1024(e.g., thee ambient air supplied to the enclosed space at 1028 is freshambient air). In an embodiment, the ambient air may be supplied to theenclosed space 1028 through the ventilation pathway. The ambient airdirected from the ambient environment into ventilation pathway, passedthrough the ventilation pathway, and then discharged (asconditioned/cooled ambient air) from the ventilation pathway in to theenclosed space. For example, in an embodiment, the ambient air isdirected through the ventilation pathway at 1028 by being by-passedaround the CO₂ scrubber (e.g., through by-pass 160). The supplying ofthe ambient air 1028 can include operating/actuating an ambient airinlet (e.g., ambient air inlet 116) to be open. The ambient air inlet isclosed when air is being scrubbed by the CO2 scrubber at 1016 such thatno ambient air is supplied into the enclosed space. For example, thefirst mode 1010 in which the CO₂ scrubber is operating in an adsorptionmode is configured to not supply/add ambient air into the enclosedspace.

It should be appreciated that the method 1000 in an embodiment may bemodified based on the MTRS 1 as shown in FIG. 1 , the transport unit 100as shown in FIGS. 2 and 3 , and/or the CO2 scrubber 140 as shown inFIGS. 2-3B and as discussed above.

The transport unit, the transport refrigeration system, and theoperation of thereof are described above for a marine transport unit. Itshould be appreciated that the above concepts may be generally appliedto transport units used for transporting produce such as to a differenttype of transport unit than a marine transport unit in otherembodiments. For example, the transport unit in an embodiment may be aground transport unit.

ASPECTS

Any of Aspects 1-13 may be combined with any of Aspects 14-22, and anyof Aspects 14-18 may be combined with any of Aspects 19-22.

Aspect 1. A transport refrigeration system for a transport unit, thetransport unit including an enclosed space for storing produce, aventilation pathway having an inlet and an outlet each connected to theenclosed space of the transport unit, the ventilation pathway configuredto direct air to flow from the enclosed space into the ventilationpathway via the inlet and out of the ventilation pathway through theoutlet, and the transport refrigeration system comprising: a refrigerantcircuit including a compressor, a condenser, an expander, and anevaporator fluidly connected, the evaporator disposed in the ventilationpathway and configured to cool air flowing through the ventilationpathway; and an CO₂ scrubber containing a metal organic framework (MOF)configured to adsorb CO₂, the CO₂ scrubber disposed in the ventilationpathway downstream of the evaporator, the CO₂ scrubber having: anadsorption mode in which the air flows over the MOF and the MOF adsorbsCO₂ from the air, and a regeneration mode in which ambient air flowsover the MOF and the adsorbed CO₂ desorbs into the ambient air.Aspect 2. The transport refrigeration system of Aspect 1, wherein thetransport refrigeration system is configured to decrease a concentrationof CO₂ in the enclosed space using the CO2 scrubber and withoutsupplying ambient air into the enclosed space.Aspect 3. The transport refrigeration system of either one of Aspects 1and 2, wherein the transport refrigeration system is configured toadjust a concentration of oxygen in the enclosed space by supplyingambient air into the enclosed space.Aspect 4. The transport refrigeration system of any one of Aspects 1-3,wherein the CO₂ scrubber is configured to maintain a concentration ofthe CO₂ in the enclosed space within a predetermined range.Aspect 5. The transport refrigeration system of Aspect 4, wherein thepredetermined range is at or above 5% by volume of the CO₂ and at orless than 15% by volume of the CO₂.Aspect 6. The transport refrigeration system of either one of Aspects 4and 5, wherein the predetermined range is based on a type of theproduce.Aspect 7. The transport refrigeration system of any one of Aspects 1-6,further comprising: a heater for heating the ambient air, wherein in theregeneration mode, the heater heats the ambient air prior to flowingover the MOF.Aspect 8. The transport refrigeration system of any one of Aspects 1-7,wherein the MOF has a maximum CO₂ saturation, and the MOF is configuredto desorb at least 90% of the maximum CO₂ saturation using the ambientair at a temperature at or below 70° C. degrees.Aspect 9. The transport refrigeration system of any one of Aspects 1-8,wherein the MOF has a CO₂ adsorption capacity of at least 25 cm³ STP ofCO₂/gram of MOF at a CO₂ concentration of 15 vol %.Aspect 10. The transport refrigeration system of any one of Aspects 1-9,wherein the CO₂ scrubber includes a MOF composition comprising the MOFand 1-10 wt % of binder.Aspect 11. The transport refrigerant system of Aspect 10, wherein thebinder is polyvinyl butyral.Aspect 12. The transport refrigeration system of any one of Aspects1-11, wherein the MOF in the CO₂ scrubber is in a form of one or more ofpellets, a coating on a mesh, and a coating on a solid surface.Aspect 13. The transport refrigeration system of any one of Aspects1-12, wherein the transport refrigeration system is a marine transportrefrigeration system and the transport unit is a marine transport unit.Aspect 14. A transport unit comprising: an enclosed space for storingproduce; a ventilation pathway having an inlet and an outlet eachconnected to the enclosed space of the transport unit, the ventilationpathway configured to direct air to flow from the enclosed space intothe ventilation pathway via the inlet and out of the ventilation pathwaythrough the outlet; a transport refrigeration system configured tocondition the enclosed space, the transport refrigeration systemincluding: a refrigerant circuit including a compressor, a condenser, anexpander, and an evaporator fluidly connected, the evaporator disposedin the ventilation pathway and configured to cool the air flowingthrough the ventilation pathway, and an CO₂ scrubber disposed in theventilation pathway downstream of the evaporator, the CO₂ scrubbercontaining a metal organic framework (MOF) configured to adsorb CO₂, theCO₂ scrubber configured to have: an adsorption mode that directs the airin the ventilation pathway to flow over the MOF, the MOF adsorbing CO₂from the air, and a regeneration mode that directs ambient air to flowover the MOF, the CO₂ adsorbed in the MOF being desorbed into theambient air.Aspect 15. The transport unit of Aspect 14, wherein the transportrefrigeration system is configured to decrease a concentration of CO₂ inthe enclosed space using the CO₂ scrubber and without supplying ambientair into the enclosed space.Aspect 16. The transport unit of either one of Aspects 14 and 15,wherein the CO₂ scrubber is configured to maintain a concentration ofthe CO₂ in the enclosed space within a predetermined range.Aspect 17. The transport unit of any one of Aspects 14-16, wherein theMOF has a maximum CO₂ saturation, and the MOF is configured to desorb atleast 90% of the maximum CO₂ saturation using the ambient air at atemperature at or below 70° C. degrees.Aspect 18. The transport unit of any one of Aspects 14-17, wherein theMOF has a CO₂ adsorption capacity of at least 25 cm³ STP of CO₂/gram ata CO₂ concentration of 15 vol %.Aspect 19. A method of conditioning an enclosed space of a transportunit, the enclosed space for storing produce, the method comprising:operating a transport refrigeration system (TRS) in a first mode, thetransport refrigeration circuit including a refrigerant circuitincluding a compressor, a condenser, an expander, and an evaporatorfluidly connected, and an CO₂ scrubber containing a metal organicframework (MOF) configured to adsorb CO₂, wherein the operating of theTRS in the first mode includes: directing air from the enclosed spacethrough a ventilation pathway, cooling, with the evaporator, the airflowing through the ventilation pathway, and adsorbing, by the MOF ofthe CO₂ scrubber, CO₂ from the air cooled by the evaporator; andoperating the TRS in a second mode, which includes: directing ambientair through the CO₂ scrubber, and regenerating, with the ambient air,the MOF of the CO₂ scrubber, wherein the CO₂ adsorbed the MOF in thefirst mode is released into the ambient air in the second mode.Aspect 20. The method of Aspect 19, wherein operating in the first modeincludes the CO₂ scrubber operating in an adsorption mode, and operatingin the second mode includes the CO₂ scrubber operating in a regenerationmode.Aspect 21. The method of either one of Aspects 19 and 20, wherein theoperating of the TRS in the first mode does not add ambient air into theenclosed space.Aspect 22. The method of any one of Aspects 19-21, wherein the MOF has aCO₂ adsorption capacity of at least 25 cm³ STP of CO₂/gram at a CO₂concentration of 15 vol %.

The terminology used herein is intended to describe particularembodiments and is not intended to be limiting. The terms “a,” “an,” and“the” include the plural forms as well, unless clearly indicatedotherwise. The terms “comprises” and/or “comprising,” when used in thisSpecification, specify the presence of the stated features, integers,steps, operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, integers, steps,operations, elements, and/or components.

With regard to the preceding description, it is to be understood thatchanges may be made in detail, especially in matters of the constructionmaterials employed and the shape, size, and arrangement of parts withoutdeparting from the scope of the present disclosure. This Specificationand the embodiments described are exemplary only, with the true scopeand spirit of the disclosure being indicated by the claims that follow.

What is claimed is:
 1. A transport refrigeration system for a transportunit, the transport unit including an enclosed space for storing produceand a ventilation pathway having an inlet and an outlet each connectedto the enclosed space of the transport unit, the ventilation pathwayconfigured to direct air to flow from the enclosed space into theventilation pathway via the inlet and out of the ventilation pathwaythrough the outlet the transport, the refrigeration system comprising: arefrigerant circuit including a compressor, a condenser, an expander,and an evaporator fluidly connected, the evaporator disposed in theventilation pathway and configured to cool air flowing through theventilation pathway; and an CO₂ scrubber containing a metal organicframework (MOF) configured to adsorb CO₂, the CO₂ scrubber disposed inthe ventilation pathway downstream of the evaporator, the CO₂ scrubberhaving: an adsorption mode in which the air flows over the MOF and theMOF adsorbs CO₂ from the air, and a regeneration mode in which ambientair flows over the MOF and the adsorbed CO₂ desorbs into the ambientair.
 2. The transport refrigeration system of claim 1, wherein thetransport refrigeration system is configured to decrease a concentrationof CO₂ in the enclosed space using the CO2 scrubber and withoutsupplying ambient air into the enclosed space.
 3. The transportrefrigeration system of claim 2, wherein the transport refrigerationsystem is configured to adjust a concentration of oxygen in the enclosedspace by supplying ambient air into the enclosed space.
 4. The transportrefrigeration system of claim 1, wherein the CO₂ scrubber is configuredto maintain a concentration of the CO₂ in the enclosed space within apredetermined range.
 5. The transport refrigeration system of claim 4,wherein the predetermined range is at or above 5% by volume of the CO₂and at or less than 15% by volume of the CO₂.
 6. The transportrefrigeration system of claim 4, wherein the predetermined range isbased on a type of the produce.
 7. The transport refrigeration system ofclaim 1, further comprising: a heater for heating the ambient air,wherein in the regeneration mode, the heater heats the ambient air priorto flowing over the MOF.
 8. The transport refrigeration system of claim1, wherein the MOF has a maximum CO₂ saturation, and the MOF isconfigured to desorb at least 90% of the maximum CO₂ saturation usingthe ambient air at a temperature at or below 70° C. degrees.
 9. Thetransport refrigeration system of claim 1, wherein the MOF has a CO₂adsorption capacity of at least 25 cm³ STP of CO₂/gram of MOF at a CO₂concentration of 15 vol %.
 10. The transport refrigeration system ofclaim 1, wherein the CO₂ scrubber includes a MOF composition comprisingthe MOF and 1-10 wt % of binder.
 11. The transport refrigeration systemof claim 10, wherein the binder is polyvinyl butyral.
 12. The transportrefrigeration system of claim 1, wherein the MOF in the CO₂ scrubber isin a form of one or more of pellets, a coating on a mesh, and a coatingon a solid surface.
 13. The transport refrigeration system of claim 1,wherein the transport refrigeration system is a marine transportrefrigeration system and the transport unit is a marine transport unit.14. A transport unit comprising: an enclosed space for storing produce;a ventilation pathway having an inlet and an outlet each connected tothe enclosed space of the transport unit, the ventilation pathwayconfigured to direct air to flow from the enclosed space into theventilation pathway via the inlet and out of the ventilation pathwaythrough the outlet; and a transport refrigeration system configured tocondition the enclosed space, the transport refrigeration systemincluding: a refrigerant circuit including a compressor, a condenser, anexpander, and an evaporator fluidly connected, the evaporator disposedin the ventilation pathway and configured to cool the air flowingthrough the ventilation pathway, and an CO₂ scrubber disposed in theventilation pathway downstream of the evaporator, the CO₂ scrubbercontaining a metal organic framework (MOF) configured to adsorb CO₂, theCO₂ scrubber configured to have: an adsorption mode that directs the airin the ventilation pathway to flow over the MOF, the MOF adsorbing CO₂from the air, and a regeneration mode that directs ambient air to flowover the MOF, the CO₂ adsorbed in the MOF being desorbed into theambient air.
 15. The transport unit of claim 14, wherein the transportrefrigeration system is configured to decrease a concentration of CO₂ inthe enclosed space using the CO₂ scrubber and without supplying ambientair into the enclosed space.
 16. The transport unit of claim 14, whereinthe CO₂ scrubber is configured to maintain a concentration of the CO₂ inthe enclosed space within a predetermined range.
 17. The transport unitof claim 14, wherein the MOF has a maximum CO₂ saturation, and the MOFis configured to desorb at least 90% of the maximum CO₂ saturation usingthe ambient air at a temperature at or below 70° C. degrees.
 18. Amethod of conditioning an enclosed space of a transport unit, theenclosed space for storing produce, the method comprising: operating atransport refrigeration system (TRS) in a first mode, the transportrefrigeration circuit including a refrigerant circuit including acompressor, a condenser, an expander, and an evaporator fluidlyconnected, and an CO₂ scrubber containing a metal organic framework(MOF) configured to adsorb CO₂, wherein the operating of the TRS in thefirst mode includes: directing air from the enclosed space through aventilation pathway, cooling, with the evaporator, the air flowingthrough the ventilation pathway, and adsorbing, by the MOF of the CO₂scrubber, CO₂ from the air cooled by the evaporator; and operating theTRS in a second mode, which includes: directing ambient air through theCO₂ scrubber, and regenerating, with the ambient air, the MOF of the CO₂scrubber, wherein the CO₂ adsorbed the MOF in the first mode is releasedinto the ambient air in the second mode.
 19. The method of claim 18,wherein the operating of the TRS in the first mode does not add ambientair into the enclosed space.
 20. The method of claim 18, wherein the MOFhas a CO₂ adsorption capacity of at least 25 cm³ STP of CO₂/gram at aCO₂ concentration of 15 vol %.